The present invention relates in general to control circuits for appliances of the domestic type, and more particularly to a control circuit for a gas heated appliance such as a gas heated clothes dryer.
The domestic appliance industry is extremely competitive. As a result, manufacturers are continuously striving to lower the cost of domestic appliance products while providing long term reliability and product versitility.
For example, a gas heated clothes dryer should provide a plurality of drying temperatures for the clothes being air dried in the rotating, horizontally oriented, drum or tumbler that is a typical component of conventional domestic dryers. The provision of multiple temperatures for the air drying of clothes in the dryer usually requires the provision of a corresponding multiple of thermostatically operated switches for turning the associated gas burner on and off for predetermined time periods to heat the drying air to the required temperatures. Thus, one thermostatic switch would regulate the gas burner to provide high temperature drying, while second and third thermostatic switches would respectively regulate the gas burner to provide medium and low temperature drying. A user operated, multiposition switch allows the selection of high, medium, or low heat drying prior to the initiation of a drying cycle.
In addition to the provision of multiple drying temperatures, a domestic dryer of the gas heated type usually includes a timer mechanism for determining the length of a drying cycle. Such a timer mechanism, in combination with a selected one of the drying temperature regulating thermostatic switches, and a burner ignition and regulating circuit operating the associated gas burner generating the heated drying air, can provide automatic turn-off of the dryer after a predetermined fixed time period which has been preset by the user. A fully automatic drying cycle can also be provided wherein the drying time is automatically varied as a function of moisture level of the clothes being dried. As is well known in the art, the rate of the temperature rise of the drying air exhausted from the dryer is a function of the moisture in the clothes being dried. By monitoring the exhaust temperature of the dryer, a timer mechanism can be intermittently turned on and off for predetermined time periods, as a function of the monitored exhaust temperature, until the timer mechanism, functioning as an integrator, "times out" to terminate the drying cycle when the clothes are fully dried or nearly fully dried.
It is a purpose of the present invention to provide a simplified, low cost, gas heated appliance control circuit which, for example, could regulate a gas heated clothes dryer as noted above.